Process for preparing cyclohexanol and cyclohexanone

ABSTRACT

This invention relates to a process for preparing cyclohexanol and cyclohexanone, in particular, to a process for preparing cyclohexanol and cyclohexanone by selectively oxidizing cyclohexane with Fe/Pd catalyst in a flow of hydrogen and oxygen gases in the mixture of acetone and acetic acid.

This application is an international application PCT/KR95/00162, with aninternational filing date of Dec. 14, 1995, which entered the nationalstage in the U.S. under 35 U.S.C. § 371 as application Ser. No.09/029,661, and further claim the benefit of the Korean patentapplication No. 1995/26858, filed Aug. 28, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for preparing cyclohexanol andcyclohexanone, in particular, to a process for preparing cyclohexanoland cyclohexanone by selectively oxidizing cyclohexane with Fe/Pdcatalyst in a flow of hydrogen and oxygen gases in the mixture ofacetone and acetic acid.

Cyclohexanol and cyclohexanone are available as intermediates forsynthesizing nylon-6 and nylon-6,6 and generally produced by oxidationof cyclohexane on an industrial scale. But the conventional processes ofpreparing cyclohexanol and cyclohexanone have some deficiencies thatthese processes require a condition of high temperature over 150° C. andhigh pressure over 8 atm and its conversion is as low as 4%. Further,the product selectivity cannot exceed 80% because various decomposedoxidation-products of cyclohexane are produced from these reactions.

Because of the above problems, continuous researches on more effectiveand selective processes for preparing cyclohexanol and cyclohexanonehave been conducted. For example, European patent appln. No. 83-87,924discloses a process for preparing alcohol or ketones by oxidizingparraffinic hydrocarbons in a reaction system which employs ironcatalyst, hydrogen sulfide, acetic acid, pyridine solvent and oxygen.But the resulting mixture shows poor separation and recovery of catalystand products and especially, a large amount of pyridine is used comparedto the amount of reaction product. Therefore, the problems of economicaldeficience and toxicity were raised.

As another example, in Japanese patent unexamined publication 85-92,236,cyclohexanone was acquired by adding oxygen to cyclohexene but thereremains a problem that the manufacture of cyclohexene is more difficultthat that of cyclohexane.

Additionally, the inventors of this invention discloses in U.S. Pat. No.5,208,392 a method for preparing cyclohexanol and cyclohexanone withabout 3˜7% yields with no byproducts, by the oxidation of cyclohexane inhydrogen and oxygen gases with Fe/Pd catalyst in acetone solvent.

This invention is an improvement of U.S. Pat. No. 5,208,392 in that theactivity and the stability of catalyst are improved through ligandbinding with iron catalyst by using the solvent mixture of acetone andacetic acid instead of pure acetone solvent. As the result, yields ofcyclohexanol and cyclohexanone increased significantly compared withthose of U.S. Pat. No. 5,208,392. And especially, the more reaction timeis extended and the more yields increase greatly up to about 4˜12%because the deactiviation of catalyst is reduced. Moreover, there islittle or nothing of byproducts during the oxidation of cyclohexane andthe recovering and reusing of solid Fe/Pd catalyst is very easy.

SUMMARY OF THE INVENTION

The object of this invention is to provide a new process for preparingcyclohexanol and cyclohexanone with high yields.

This invention is characterized in using the mixture of acetone (1weight parts) and acetic acid (0.05˜1.5 weight parts) in preparingcyclohexanol and cyclohexanone by oxidation of cyclohexane with Fe/Pdcatalyst.

DETAILED DESCRIPTION OF THIS INVENTION

This invention is based on the catalytic abilities, that is, that ofpalladium catalyst is to convert molecular hydrogen and oxygen added tothe solvent into hydrogen peroxide; and that of iron catalyst is to usethe said hydrogen peroxide in the oxidation of hydrocarbons and it ischaracterized in using the mixture of acetone and acetic acid as asolvent. The said acetic acid acts as a ligand for iron catalyst andplays a role to improve the activity and the stability of iron catalyst.

In this invention, iron and palladium are used as catalysts and they canbe used respectively or properly mixed together as solid catalysts.

The iron catalyst of this invention employs iron salt such as Fe²⁺ orFe³⁺, or iron oxide such as FeCl₂, FeCl₃, FeO, Fe₂ O₃, FeSO₄, Fe₂ (SO₄)₃or Fe(OAc)₂ with no special pretreatment. And the palladium catalyst ofthis invention employs palladium metal or palladium salts (for example,PdCl₂, Pd(NO₃)₂ etc.) supported by an appropriate carrier which isselected from alumina, silica, silica-alumina and carbon.

The ratio of iron and palladium used as catalysts in this reaction ispreferable to be 0.02˜1 weight parts of palladium to 1 weight parts ofiron. It is not desirable to use a large amount of palladium catalystbecause the rate of decomposing the produced hydrogen peroxide by thepalladium catalyst becomes larger than that of using the producedhydrogen peroxide by the iron catalyst.

The solid Fe/Pd catalyst can be prepared by impregnating a solution ofpalladium compound onto iron oxide (for example, FeO, Fe₃ O₄, Fe₂ O₃etc.). Explained more in detail, after preparing the solution of apalladium compound such as palladium chloride or palladium nitrate, itis impregnated onto an iron oxide, dried at 100˜150° C. for 2˜24 hoursand calcined at 300˜600° C. for 2˜15 hours in a flow of air or hydrogen.Thus the solid state catalyst is prepared. The prepared solid catalystis pretreated to increase its activity before used in the preparation ofcyclohexanol and cyclohexanone. The pretreatment is to contact 1 weightparts of solid catalyst with the mixed gases of hydrogen and oxygen for10˜50 hours in the solution of 1˜20 weight parts of cyclohexane and 4˜50weight parts of acetone-acetic acid mixture and dry it at 80˜150° C. for10˜30 hours. The acetone and acetic acid used in the pretreatment isprepared by mixing 1 weight parts of acetone with 0.05˜1.5 weight partsof acetic acid and hydrogen and oxygen gases are respectively providedat a rate of 0.2˜10 by volume per minute.

In this invention, another important thing is to use a proper reactionmedium such as acetone and acetic acid mixture. If acetone is not usedin reaction medium, all the reacting compounds such as hydrogenperoxide, hydrogen, oxygen and cyclohexane cannot be dissolved evenlyand the reaction cannot be proceeded efficiently. And if acetic acid isnot mixed, high yields and efficient reuse of the catalyst, which arecharacteristics of this invention, cannot be expected. The ratio ofacetone and acetic acid is preferable within the range from 1:0.05 to1:1.5 by weight. If the acetic acid is used in large amount, the solventeffect for evenly dissolving the reactants becomes low.

In this invention, the cyclohexanol and cyclohexanone is prepared byadding the above-mentioned Fe/Pd catalyst to the solution ofacetone-acetic acid and flowing hydrogen and oxygen gases to it. And atthis time, it is desirable to use cyclohexane in an amount of 1˜20 timesof the Fe/Pd catalyst by weight and the mixture of acetone and aceticacid in an amount of 4˜50 times of the Fe/Pd catalyst by weight isdesirable. If cyclohexane is used less than 1 times of the total amountof the Fe/Pd catalyst by weight, the reaction system becomes inefficientbecause the amount of products, which can be produced for the reaction,is too small compared with the amount of catalyst. And if it is morethan 20 times by weight, the reaction slows down because the amount ofcatalyst becomes too small compared with the amount of the reactants. Ifthe used amount of acetone and acetic acid mixture is less than 4 timesby weight, the yield increase by the reaction-medium effect is not givenbecause the amount of reaction medium becomes too small compared withthe whole amount of reaction system and if it exceeds 50 times inweight, reaction rate cannot be expected to be efficiently high becausethe concentration of catalyst and reactants become too low. And thehydrogen and oxygen gases may be respectively provided at a rate of0.2˜10 by volume per minute to solution and dissolved. But at this time,if the each amount of flowed hydrogen and oxygen is less than 0.2 byvolume per minute, the yields are decreased due to low concentrationthereof and if it exceeds 10 by volume per minute, the reaction systembecomes inefficient because the gas flow is too high to be dissolved.The reaction is carried out under a mild condition, e.g. at anatmospheric pressure and at a temperature between 10˜50° C. and thereactant and the solvent evaporated during the reaction is reused byrefluxing in a refrigerated condenser.

As explained in the above, the process of preparing cyclohexanol andcyclohexanone in this invention by oxidizing cyclohexane with hydrogenand oxygen gases is characterized in that Fe/Pd catalyst is used as acatalyst and the mixture of acetone and acetic acid is used as asolvent. And compared with the conventional processes, the yield in thisinvention is greatly increased and especially in long time reaction, theincrease is noticable because the deactivation of catalyst can beprevented.

This invention is illustrated by the following Examples, which shouldnot be taken to limit the scope of the invention. And the yields arecalculated by the following equations; ##EQU1##

EXAMPLE 1

After adding FeCl₂ ·4H₂ O (0.3 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (17 ml) and acetic acid (3ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 3.94 mole % of cyclohexanol and 0.83mole % cyclohexanone with the total yield of 4.77 mole % were obtained.

EXAMPLE 2

After adding FeCl₂ ·4H₂ O (1 g), Pd/alumina(Pd content 1%, 3 g) andcyclohexane (5 g) to the mixture of acetone (17 ml) and acetic acid (3ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 6.83 mole % of cyclohexanol and 1.24mole % cyclohexanone with the total yield of 8.07 mole % were obtained.

EXAMPLE 3

After adding FeCl₂ ·4H₂ O (0.5 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (17 ml) and acetic acid (3ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 17 hours at30° C. under atmospheric pressure, 8.84 mole % of cyclohexanol and 2.13mole % cyclohexanone with the total yield of 10.97 mole % were obtained.

EXAMPLE 4

The reaction is carried out in the same manner as in Example 3 exceptthat the reaction time was 24 hours, and in result, 8.21 mole % ofcyclohexanol and 3.32 mole % cyclohexanone with the total yield of 11.53mole % were obtained.

EXAMPLE 5

After adding FeCl₂ ·4H₂ O (0.1 g), Pd/alumina(Pd content 2%, 1 g) andcyclohexane (5 g) to the mixture of acetone (20 ml) and acetic acid (1ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 4.03 mole % of cyclohexanol and 0.65mole % cyclohexanone with the total yield of 4.68 mole % were obtained.

EXAMPLE 6

After adding FeCl₂ ·4H₂ O (0.3 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (19 ml) and acetic acid (1ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 3.50 mole % of cyclohexanol and 0.62mole % cyclohexanone with the total yield of 4.12 mole % were obtained.

EXAMPLE 7

After adding FeCl₂ ·4H₂ O (0.3 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (15 ml) and acetic acid (5ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at35° C. under atmospheric pressure, 4.01 mole % of cyclohexanol and 0.74mole % cyclohexanone with the total yield of 4.75 mole % were obtained.

EXAMPLE 8

After adding FeCl₂ ·4H₂ O (0.3 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (10 ml) and acetic acid (10ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at36° C. under atmospheric pressure, 3.40 mole % of cyclohexanol and 0.69mole % cyclohexanone with the total yield of 4.09 mole % were obtained.

EXAMPLE 9

After adding FeCl₃ ·6H₂ O (0.4 g), Pd/alumina(Pd content 1%, 1 g) andcyclohexane (5 g) to the mixture of acetone (17 ml) and acetic acid (3ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 4.22 mole % of cyclohexanol and 0.80mole % cyclohexanone with the total yield of 5.02 mole % were obtained.

EXAMPLE 10

After adding Fe₂ O₃ (1 g), Pd/silica (Pd content 1.3%, 1 g) andcyclohexane (5 g) to the mixture of acetone (20 ml) and acetic acid (1ml), it was stirred in a flow of hydrogen and oxygen gases at therespective rate of 20 ml/min. As the result of reaction for 3 hours at30° C. under atmospheric pressure, 3.13 mole % of cyclohexanol and 0.41mole % cyclohexanone with the total yield of 3.54 mole % were obtained.

EXAMPLE 11

In 1.6 g of PdCl₂ in water(160 ml), Fe₂ O₃ (8 g) was added andimpregnated by evaporation. When the evaporation of water was completed,it was dried at 150° C. for 1.5 hours and calcined in a flow of themixed gas of hydrogen and nitrogen(5% H₂ +95% N₂) at 500° C. for 4 hoursand at 500° C. for 8 hours in a flow of air. As the result of reaction,Pd/Fe₂ O₃ catalyst was prepared.

After adding cyclohexane (5 g), acetone 17 ml) and acetic acid (3 ml) toPd/Fe₂ O₃ (1 g), it was stirred in a flow of hydrogen and oxygen gasesat the respective rate of 20 ml/min. As the result of reaction for 16hours at 30° C. under atmospheric pressure, 3.63 mole % of cyclohexanoland 2.45 mole % cyclohexanone with the total yield of 6.08 mole % wereproduced.

EXAMPLE 12

After adding cyclohexane (5 g), acetone (17 ml) and acetic acid (3 ml)to Pd/Fe₂ O₃ (1 g), which was prepared by the same manner in Example 11,it was stirred at 30° C. for 48 hours in a flow of hydrogen and oxygengases at the respective rate of 20 ml/min., filtered and dried for 24hours in oven of 120° C. in order to activate the catalyst. To theactivated catalyst (1 g), cyclohexane (5 g), acetone(17 ml) and aceticacid (3 ml) were added and stirred in a flow of hydrogen and oxygengases at the respective rate of 20 ml/min. As the result of reaction for16 hours at 30° C. under atmospheric pressure, 4.25 mole % ofcyclohexanol and 7.25 mole % cyclohexanone with the total yield of 11.50mole % were obtained.

COMPARATIVE EXAMPLE 1

1.3 mole % of cyclohexanol and 0.27 mole % cyclohexanone with totalyield of 1.57 mole % were obtained by the same manner in Example 1except that pure acetone (20 ml) was used as solvent instead of theacetone and acetic acid mixture.

COMPARATIVE EXAMPLE 2

0.58 mole % of cyclohexanol and 0.20 mole % cyclohexanone with the totalyield of 0.78 mole % were obtained by the same manner in Example 1except that pure acetone (20 ml) was used as solvent instead of theacetone and acetic acid mixture.

COMPARATIVE EXAMPLE 3

The catalyst was activated by the same manner with Example 12 exceptthat pure acetone (20 ml) was used as solvent instead of the acetone andacetic acid mixture. 1.76 mole % of cyclohexanol and 0.77 mole %cyclohexanone with the total yield of 2.53 mole % were obtained by thesame manner in Example 5 except that pure acetone (20 ml) was used assolvent instead of the acetone and acetic acid mixture.

What is claimed is:
 1. A process for preparing cyclohexanol andcyclohexanone by oxidizing cyclohexane with an Fe/Pd catalyst in a flowof hydrogen and oxygen gases, and in the presence of a mixture ofacetone and acetic acid wherein the ratio of acetone to acetic acidranges from 1:0.05 to 1:1.5 by weight.
 2. The process of claim 1,wherein the mixture of acetone and acetic acid is in an amount of 4 to50 times by weight of the Fe/Pd catalyst.
 3. The process of claim 1,wherein cyclohexane is in an amount of 1 to 20 times by weight of theFe/Pd catalyst.
 4. The process of claim 1, wherein the Fe/Pd catalyst isa mixture of a palladium compound supported by a carrier and an ironbased compound.
 5. The process of claim 4, wherein the iron basedcompound is selected from the group consisting of FeCl₂, FeCl₃, FeO, Fe₂O₃, FeSO₄, Fe₂ (SO₄)₃, and Fe(OAc)₂.
 6. The process of claim 4, whereinthe carrier is selected from the group consisting of alumina, silica,silica-alumina, and carbon.
 7. The process of claim 1, wherein the Fe/Pdcatalyst is prepared by impregnating a palladium compound onto an ironoxide, followed by drying the impregnated iron oxide, and then calciningthe dried oxide under air or hydrogen.
 8. The process of claim 7,wherein the iron oxide is FeO, Fe₃ O₄, or Fe₂ O₃.
 9. The process ofclaim 7, wherein the palladium compound is PdCl₂ or [Pd(NO₃)₂ ].
 10. Theprocess of claim 7, wherein the catalyst is activated.